Known conventional methods to introduce a formyl group into an aromatic ring are to react alkyl lithium, such as n-butyl lithium, with N,N-dimethylformamide (DMF) or N-phenyl-N-methylformamide, to react alkyl lithium with formate, such as methyl formate, and the like.
For example, European Patent Laid-open specifications Nos. 125803 and 174131 describe a method to react 2,5-difluorobenzotrifluoride with n-butyl lithium and N-phenyl-N-methylformamide. However, this formylation reaction usually gives two reaction products, not being selective.
In the case of the reaction of 3,4-dichlorobenzotrifluoride with n-butyl lithium and DMF, 2,3-dichloro-5-trifluoromethylbenzaldehyde is the main product, as described later.
In the Japanese Patent Laid-open No. Hei 3-5436 Gazette, compounds represented by the general formula (Ia), which contain the compounds of this invention, are described. ##STR2##
Conventionally 2,3-dihalogeno-6-trifluoromethylbenzamidoximes have been produced via 2,3-dihalogeno-6-trifluoromethylbenzonitrile (refer to WO/19442 Gazette). However, this method had problems of low yield and long reaction processes.